Abstract: The present invention relates to a dimension reducing flange equipped nut insert (2) to quickly and safely releasably insertion in a tool head (1) of an hydraulic wrench. The invention is characterized by at least two inserts (3) of a magnetic material intended to, at a mounted position of the insert, come to a close position towards magnetisable portions of the tool head (1) in such a way to allow a magnetic flow between the parts and exert a retaining action between the nut socket insert (2) and the tool head (1).